Proton Therapy (PT) is a cancer treatment technology that uses high energy protons to penetrate a patient's body and deposit energy into treatment volumes such as cancerous tumors. PT leverages the Bragg Peak property of charged particles where they deposit the majority of the energy in the last few millimeters of travel as opposed to conventional radiation therapy where the majority of energy is deposited in the first few millimeters of travel—which often causes significant damage to healthy tissue.
PT is delivered to patients through a series of treatments, which frequently occur every day for several weeks. Each treatment typically requires an anatomical image to verify that the tumor is in the correct position prior to treatment, which may be done with basic planar x-ray technology. The most common beam delivery technique is double scattering where a narrow proton beam is scattered to spread the protons physically and also to create an energy spread such that the protons are traveling at various energies. A collimator may be used to trim the proton treatment area in x and y dimensions, and a compensator may be used to modify the proton treatment in the z dimension. The protons are trimmed to the shape of the tumor to precisely deliver the radiation dose to the treatment volume, while sparing the surrounding healthy tissue.
In contrast, a more advanced technique that is gaining popularity is Pencil Beam Scanning (“PBS”), which eliminates the beam scattering, collimator, and compensator. In PBS treatments, the narrow proton beam is directed by a scanning magnet to follow the treatment shape in the x and y dimensions. The beam is adjusted in the z dimension by varying the energy with an energy degrader, frequently positioned between the scanning magnet and the particle accelerator, such as a cyclotron, generating the proton beam.